The purpose of this study is to investigate the fluctuating response to L-DOPA, the so-called "on-off" phenomenon. We will examine parkinsonian signs, blood pressure, mood and anxiety and measure blood L-DOPA, L-DOPA breakdown products and amino acids every half to three hours while patients are receiving L-DOPA orally or while receiving it by vein. The results of these studies may help design better treatments for parkinsonism. The estimated enrollment is approximately 40 subjects in this study. No single subject participates in all procedures.